This invention relates to a brush shroud assembly for a gas turbine engine.
A gas turbine engine for an airplane has an outer air seal made of segments. These outer air seal segments form a circular cover or case around the rotating blades of a compressor or turbine. A gap is necessary between the case and blade to prevent the tips of the blades from contacting the case and being damaged. However, this gap reduces the efficiency of the turbine engine by permitting the creation of turbulence and air leakage at the tips of the blades. It is desirable to reduce the space between the outer air seal segment and the rotating blade so as to reduce this turbulence.
Airplane manufacturers have used plasma spray coatings, feltmetal or rubber between the outer air seal segment and the blade for this purpose. During a break-in period, the blades rub up against these abradable surfaces to provide sufficient clearance for rotation of the blades while providing a seal against turbulence and air leakage between the blade and the outer air seal segment. Typically, worn abradable surfaces are restored as part of an engine overhaul.
More recently, manufacturers have begun using bristle brushes formed as part of the outer air seal segment. Because bristle brushes are formed as part of the outer air seal segment, they are expensive and potentially difficult to replace. Furthermore, the outer air seal segments are specific to the particular design and size of the turbine engine. For example, one outer air seal segment having a brush may fit one particular diameter of turbine engine but not another because the outer air seal segment has a curvature conforming to the specific sized radius of the turbine engine. As a consequence, replacement of the brush requires replacement of the entire outer air seal segment or its repair. A need therefore exists for improved sealing assemblies.